ECU Gearbox Fault code U1209 (DS3 Citroen) Auto & Limp mode

[odysseik]

Hi there,

My Citroen DS3 2014 Auto and has an issue that randomly throws the car in Limp mode at least once every 5-10 miles. The local garage diagnostic(non Lexia) showed U1209 CAN Network communication problem with the Gearbox ECU.

Any help please? I just bought the car 1 month ago, is used car.

From experience, what could it be the issue?; expensive?

[GiveMeABreak]

Pop the VIN up (automasked) so we know exactly what you have, but U1209 generally means that the communication between the gearbox ECU and the ESP ECU is missing, which points to a fault with the Automatic Gearbox ECU or a wiring connection somewhere along the network. I'll be able to confirm once you provide your VIN.

[pablo95]

Hello. I'm getting error U1209. People write on the Internet that it can appear for various reasons:
- ABS system malfunction (it is necessary to check the ABS sensors, chips on the rings, etc.)
- Damage to the wiring to the automatic transmission control unit or poor contact (it is possible to clean the connection contacts to the automatic transmission unit and check wiring

It was useful to read errors because one problem shook me:
An error of the recoil system crashes, then the ESP icon lights up and writes "Handbrake failure ..." in the on-board computer. At the same time, instead of the number of the selected gear, a dash is drawn on the panel. If it stops, transfer to "P" and re-enable "D", then the transmissions begin to be displayed. This can happen both in motion and when warming up in the parking lot (when shifting gears).
All this horsemanship is manifested not constantly and chaotically.
A month ago I gave the car to paint the rear bumper. So, the car was thoroughly washed, and it stood in a warm box for 5 days. After that, I rode for almost a month without the above jambs. I'm inclined to believe that the car just dried out with all the consequences and that's why it was normal.

I would like to find the cause on my own. Please tell me who is in the subject:
1. How to clean the ABS sensors and rings?
2. How to ring the ABS sensor (as I understand it, check the resistance with a multimeter)
3. Where is the automatic transmission control unit located (I want to clean the contacts)

Update
03/04/2019: Ride to the dealer. Hour poking around, as a result voiced a mistake that I already knew for 1200 rubles . They said it would take a whole day to find the cause. Recorded for Saturday. They added that I have some wiring problems, I need to call.
03/10/2019: The dealer was tinkering with the car for 3 hours. They said that they cleaned up the masses as much as they could, adjusted the automatic transmission gearshift device. In BC, the error u1209 remained, but the errors of the parking brake and ABS with ESP no longer climbed out.

[odysseik]

Pop the VIN up (automasked) so we know exactly what you have, but U1209 generally means that the communication between the gearbox ECU and the ESP ECU is missing, which points to a fault with the Automatic Gearbox ECU or a wiring connection somewhere along the network. I'll be able to confirm once you provide your VIN.

The VIN is: VF7**************[VIN obfuscated, can be read by forum staff]

[odysseik]

Forgot to also mention that randomly Snow and Sport mode signs are flashing on the dashboard as also instead of D(drive) shows a dash(-).

[GiveMeABreak]

Ok, that is important information.

You have the AL4 Auto gearbox. Is the SERVICE light on or GEARBOX FAULT message being shown as well as the flashing Sport and Snow lights?

This could be a problem with the oil wear counter having exceeded 32958 units. If this is the case then the recommendation is to change the gearbox oil as soon as possible. There is a proper procedure to do this and you need a diagnostic tool to do it like Diagbox as the oil counter will also need resetting afterwards.

Fault Code:	U1209
Description of Fault:	Communication with the automatic gearbox ECU missing. Data invalid. Information from the gearbox invalid.
Conditions for Fault to clear:	After switching the ignition off and then back on
Downgrade Modes whilst Fault is active:	Cutting of all ESP operations
Symptoms:	-
Suspect Areas:	Automatic gearbox ECU

Having looked at the fault code above, yiu can see there is a problem with the gearbox ECU communication. So with these 2 faults, it is hard to know if they are related. With both of these issues together, it needs further investigation as to whether they are separate problems or whether the flashing gearbox lights are related to the fault code.

I would address the fault code first and get the gearbox ECU checked out and then see if this cures the flashing gearbox lights, as fault codes should be addressed first of all.

[odysseik]

First time it occurred (the flashing of Snow/Sport mode) it was showing a message "Gearbox Fault" on the 'radio screen' of the car.

[GiveMeABreak]

Ok, so follow my advice and get it fully diagnosed. Officially, you should resolve the fault code first and then get the oil replaced in the gearbox.

[odysseik]

Ok, so follow my advice and get it fully diagnosed. Officially, you should resolve the fault code first and then get the oil replaced in the gearbox.

Thanks for your help! I didn't even knew you have to replace the gearbox oil in this car. I'll get some Citroen specialist to diagnose it first.

[GiveMeABreak]

Officially they say the gearboxes are sealed for life - but this is not true, They will last a lot longer and operate much better if the oil is changed every 50k miles at least. You can only partially drain and refill the auto gearboxes as a lot of the oil remains in the torque converter, so it can't fully be changed. Several changes over 2-3 months is generally the best way to do as full a change as you can. But in your case if the oil is dirty it will affect the operation and can lead to faults. But as I said when they diagnose it they will also be able to check the fault code too.

[odysseik]

Sorry I didn't get that, what do you mean by "Several changes over 2-3 months is generally the best way to do as full a change as you can". I suppose to be changing the gearbox oil all the time in other words :O ?

[Hell Razor5543]

There will be oil trapped in the torque converter. It is not possible to get all of the oil out in one go (unless you remove and dismantle the gearbox, of course). This means that, when you do ONE oil change, you are actually only getting out about half of the total amount of oil. This is why it is recommended to change the oil a few times over the space of a couple of months, so you will, in that time, reduce the amount of 'old' oil to about 1/16th after four oil changes.

There are companies who do a 'hot flush' which they say will completely get rid of the old oil. This (I believe) is done with the engine running (and possibly in gear on a rolling road) so the torque converter is active and not retaining the oil. I do not know WHO does this, or how much it costs.

[odysseik]

I see. Thanks. I'll take it for Lexia diagnostic and show all the information I have from this post to the mechanic and take it from there.

[odysseik]

Update: I took it for Lexia diagnostic. The only Fault found showed in the category of Transmission but it was just Brake Light Switch fault.

So just to recap; We have symptoms: 1. Randomly and rarely going into limp mode for a minute or less or until reset. 2. There used to be * and Sport mode flashing, not anymore(somehow) 3. Still sometimes I get a Dash(-) instead of D(drive) randomly 4. In the screen I saw once a "gearbox fault" warning. But its been over a month now that I haven't seen that.

Car drives fine overall, gearbox is smooth and nice and no issues at all (apart of the random limp modes- ughh.) Brake lights work fine as far as I can tell.

BUT, we have 2 faults found in total: 1. CAN Network communication fault with the Gearbox ECU from generic diagnostic, and 2. Brake Light Switch fault from Lexia diagnostic.

Mechanic is confident and said that once we change the brake light switch problem will be solved. According to the faults I do believe that the brake switch wiring that sends signal to the gearbox ECU (to let it know that we are braking so gear changing can be released; as is automatic) is faulty.

What do you guys think?; should I go ahead and change the brake light switch and see if that fixes it or do you think that is definitely something more??

[Hell Razor5543]

Yes, the brake light switch does more than just trigger the brake lights, so a faulty switch can cause the ECUs to get 'confused'. You can probably get a decent replacement switch from GSF for around £10. Make sure to get a decent switch, rather than a cheapo, as it (potentially) will save you hassle in the future.